The present invention concerns a timepiece including a case provided with a back cover and a middle part, as well as a casing ring arranged to contain a movement fitted with hands moving above a dial, the ring extending over substantially the entire height of the middle part into which it is fitted.
Assembling a watch usually includes the following steps in succession. First of all, the movement is introduced into the casing ring by orienting these two parts so that, if the parts are round, a raised portion of the casing ring penetrates a recess of the movement. Secondly, a dial is placed on the ring. When the dial is pressed against the ring, the latter is definitively secured for example by ultrasound welding. The hands of the movement are then set in place. The casing ring is then introduced via the top of the case and it is made to slide until it abuts against the back cover thereof. The movement also includes a time-setting stem onto which a crown is fitted. This time-setting stem assures the angular orientation of the ring with respect to the middle part when the watch is being assembled, in the event that the middle part and the ring have a round configuration. It will be understood that, in such case, the holes made respectively in the middle part and the casing ring have to be aligned to allow the time-setting stem to pass through. The watch also includes a crystal mounted above the dial and secured to the case by means of a bezel engaged in a notch provided in the upper periphery of the middle part.
The assembly method which has just been described has the drawback that it is difficult, because of plays inherent in the dimensional tolerances of the dial, the casing ring and the back cover of the case, to assure a determined and precise height position of the movement with respect to the case. In certain cases, the vertical play of the ring with respect to the case can be recovered due to the pressure exerted by the bezel under the effect of which the ring tends to become elastically deformed. However, this occurs at the cost of a constant reaction pressure of the ring against the crystal which is then liable to become damaged or to slip out of the middle part.
In order to overcome this drawback and to allow more precise height positioning of the casing ring with respect to the case, providing the circle with means able to deform plastically to remove all dimensional play has been proposed. An embodiment example of such a ring is shown in FIGS. 1 and 2 annexed to the present Patent Application.
With reference to FIG. 1, one sees a cross-section of a timepiece designated as a whole by the general numerical reference 1. This timepiece 1 includes a movement 2 mounted in a casing ring 4, a dial 6 mounted above a casing ring 4 and a crystal 8 mounted above dial 6. Casing ring is mounted in a case 10 including a middle part 12 and a back cover 14 made in one piece with middle part 12. Crystal 8 rests on the top of middle part 12 and is secured thereto by a bezel 16 held in a notch 18.
The means allowing circle 4 to be positioned in height with respect to case 10 consist in a plurality of points 20 only one of which is shown in FIG. 1. These points 20 in the shape of cones are arranged under casing ring 4. They are, for example, four in number, arranged at an equal distance from each other to assure casing ring 4 is well seated on back cover 14. After setting in place casing ring 4 in case 10, the latter is pushed. Under the effect of this pressure, points 20 are crushed and deform plastically against back cover 14 of case 10, until casing ring 4 occupies a determined height position with respect to case 10. At that moment, cones 20 end, no longer in points, but in bulges as can be seen in FIG. 1, and more precisely still in FIG. 2 which is a detailed view of FIG. 1.
As will have been understood from the foregoing, the positioning means described above undergo plastic deformation, this deformation resulting in crushing the material irreversibly. Thus, when the casing ring is in place, it does not undergo any vertical pressure as is the case when it undergoes plastic deformation.
When used, the solution which has just been described, although constituting substantial improvement with respect to the state of the art, has nonetheless revealed certain drawbacks. In particular, it has been realised that the positioning means do not always allow the height of the casing ring to be adjusted with respect to the middle part as precisely as was wished. It will be understood that it is difficult to control rigorously the crushing and deformation of the points via which the casing ring rests on the back cover of the case. It has thus been observed that, in certain cases, it was not possible to align the holes made in the middle part and the casing ring in a suitable way for the passage of the time-setting stem. The stem thus tended to become blocked by seizing, which made the handling thereof difficult, or impossible.
The object of the present invention is to overcome the aforementioned drawbacks of the prior art by providing a timepiece including a casing ring able to be positioned with precision in the case and not exerting pressure in a way likely to remove the crystal from its housing.
The present invention thus concerns a timepiece including a case provided with a back cover and a middle part, a movement mounted in the casing ring, a dial mounted above the ring and a crystal mounted above the ring, this crystal being provided with an annular collar surrounding the flank of the dial, characterised in that the casing ring includes means arranged to remove all the play inherent in the dimensional tolerances of the dial, the ring and the back cover, these means on which the collar of the crystal is supported being arranged at the upper end of the ring, along the outer circumference thereof.
According to another feature of the invention, the means for removing the play due to the different dimensional tolerances are flexible strips able to be elastically deformed.
As a result of these features, it is possible to assure precise positioning of the movement with respect to the case. It is no longer necessary for the casing ring to be made of a material subject to plastic deformation as was the case in the prior art. The ring and the back cover of the case can then be machined with a high level of precision, typically of the order of several hundredths of a millimetre, compatible with good alignment of the time-setting stem passage holes which are made in the middle part and the ring. At the same time, any play due to the dimensional tolerances of the different parts (ring, dial, case back cover) is eliminated by the elastic deformation of the flexible strips arranged at the top end of the casing ring on which the crystal collar is supported. The sum of the different tolerances is substantially less than the deformation amplitude of the flexible strips which is of the order of two to three tenths of a millimetre. Thus, when the crystal is arranged above the ring and it its secured thereto by means of the bezel driven into a notch of the middle part, it abuts the strips, which has the effect of pressing the ring against the back cover of the case. Consequently, whether the play is positive or negative, the ring and the crystal are always suitably held in the case of the timepiece.